Nanoparticles are important components in the development of catalytic, sensor, aerosol, filter, biomedical, magnetic, dielectric, optical, electronic, structural, ceramic, and metallurgical applications.
Various processes to produce nanoparticles, including semiconductor and metal nanoparticles, are known in the prior art. For example, U.S. Pat. No. 5,543,133, issued to Swanson et al., discloses a process of preparing nanoparticulate agents comprising the steps of: (i) preparing a premix of the agent and a surface modifier; and (ii) subjecting the premix to mechanical means to reduce the particle size of the agent, the mechanical means producing shear, impact, cavitation and attrition.
Likewise, U.S. Pat. No. 5,585,020, issued to Becker et al., teaches a process of producing nanoparticles having a narrow size distribution by exposing microparticles to an energy beam, such as a beam of laser light, above the ablation threshold of the microparticles.
Also, U.S. Pat. No. 5,879,750, issued to Higgins et al. teaches a process for producing inorganic nanoparticles by precipitating the inorganic nanoparticles by a precipitating agent for a microemulsion with a continuous and a non-continuous phase and concentrating the precipitated nanoparticles employing an ultrafiltration membrane.
Additionally, U.S. Pat. No. 6,540,495, issued to Markowicz et al., teaches a process for making a powder containing metallic particles comprising the steps of: (i) forming a dispersion of surfactant vesicles in the presence of catalytic metal ions; (ii) adjusting the pH to between 5.0 and 7.0; (iii) mixing the dispersion with a bath containing second metal ions; and (iv) incubating the mixed dispersion at a temperature sufficient to reduce the second metal ions to metal particles having an average diameter between 1 to 100 nm.
CS Pro Systems advertises a high voltage AC processor producing nanoparticles of colloidal silver. The HVAC process is claimed to produce particle sizes between 0.002 to 0.007-9 microns by imposing an AC potential of 10,000 volts across two silver electrodes in a distilled water medium.
More recently, U.S. Pat. No. 6,848,565, issued to Korgel et al., disclosed a method for fabricating semiconductor nanoparticles by heating a mixture of an organometallic precursor and a capping agent at a temperature wherein the precursor decomposes, and the nanoparticles are formed.
Still more recently, U.S. Pat. No. 7,128,816, issued to Denes et al., describes a method and apparatus for producing colloidal dispersions of conductive nanoparticles by generating a plasma reaction in a dense fluid medium between two electrodes, one of which is a rotating electrode.